It is often desirable to provide people with visual information. Frequently, one wishes to superimpose such visual information upon a view of the real world. In other applications, it is desired to shield the user from a view of the environment, providing an exclusive view of the visual information. Such displays may include a number of components including, in a form known as a folded catadioptric display, an image generator, a beam splitter which receives the image light from the image generator, often via a series of lenses and other optic elements and sends a fraction, designated the reflected fraction, of such image light to a reflective combiner that is either non-transmissive or both allows light from the real world to pass through such combiner and reflects the image light such that both the real-world light and the image light are transmitted to the eye of the user through the beam splitter, often via another series of lenses or other optical elements. The beam splitter will transmit a fraction, designated the transmitted fraction, of the image light reflected from the collimator-combiner. In embodiments in which the combiner is at least partially transmissive, a fraction of the real-world light is also transmitted by the beam splitter.
Previous devices included a number of additional components. Some devices have included corrective optical elements. Other devices have included a depixelator, e.g., as described in PCT/US94/01390 filed Feb. 7, 1994 for "Depixelated Visual Display" (incorporated herein by reference). Still other devices have included apparatus for intensifying the visual display such as those described in PCT/US94/01391, filed Feb. 7, 1994 for "Intensified Visual Display" (incorporated herein by reference).
In designing a system for providing a generated image to the eye or eyes of a user, various factors are often in opposition. Although it is desirable to provide an image which has high quality so as to not only provide a pleasing and attractive display for the user but also to reduce eyestrain, very often the techniques used to produce such a high quality image have been contrary to goals of an apparatus which is lightweight, low-cost, and relatively easy to design, fabricate and/or repair. Many previous devices have required expensive and heavy series of optical elements such as lenses to achieve a desired picture quality. Other devices have simply accepted a lower-quality image in order to achieve goals of low-cost or light weight. For example, some previous devices have failed to provide a flat focal field to the user. Others have resulted in a poor image contrast, particularly at high viewing angles of the image. Many devices have deprived the user of the full image in order to mask-off unwanted light near the edge of an image generator.
Accordingly, it would be useful to provide a personal, visual display apparatus which provides a high quality of image, which is low cost, lightweight, comfortable and has increased ease of design, fabrication, repair and the like.
In many uses of a head mounted display, it is desired to collect information regarding the position, posture, orientation, attitude, location and/or movement of the user's head. This information can be used to control the image generated to the eyes of the user for a number of purposes, such as to provide a "virtual reality" or simulated environment to the user, to allow the user to navigate through various displayed images to observe a simulated object from various angles and the like. For example, this information can be used to control the characteristics of the image shown in a head-mounted display or other virtual reality device, such as to produce changes in the image that would correspond to movement of the user's head. For example, in a flight simulator program, when the user's head rotates from a straight ahead position to a 90.degree. left position, the display should change from a display simulating a forward view, out the cockpit window, to a display simulating a view over the left wing of the aircraft.
Head trackers have been attempted in the past, such as those described in U.S. Pat. Nos. 5,373,857; and 5,345,944. However, many previous head trackers have suffered from a number of deficiencies. In some devices, head trackers were formed as an integral part of a head-mounted display and were not readily detachable. This, however, led to head-mounted displays which are heavier than necessary when used in applications where head tracking is not needed or desired. Furthermore, integral head trackers add to the cost of a head-mounted display in a manner which may be unnecessary for some uses when head tracking is not desired.
Some head tracking devices have included mounting some of the components in positions which do not provide a desirable balancing of weight in the head-mounted display device, such that there may be an undesirable neck strain for the user.
Some previous head trackers provided communication to the computer which was difficult for the end user to install and/or awkward in operation. For example, in some devices, it was required that the user install a card inside the chassis of a personal computer (PC) which, effectively, meant that many users would need to make a trip to a computer service facility.
In a configuration in which communication from the head tracker to the computer is via a cable which is separate from the head-mounted display cable, the user must wear a device which is "tethered" via two separate cables, which can tangle and inhibit free movement of the user. In devices where a single cable provides for communication of both head tracker and video information, the head tracker was not readily detachable from the head-mounted display.
In some previous devices, the output from the head tracker was provided in only a single format and the software which employed head tracker information had to be written so as to accommodate that data format.
In some devices, a head tracker used magnetic sensors. While magnetic sensors can be useful in many situations, head tracking information may be distorted by spatial variations and/or changes in the local magnetic field, such as may arise from adjustment of earphones or other audio output devices.
Accordingly, it would be useful to provide a head tracker which is of modular or detachable construction, can be located in a well-balanced position, provides for communication with the computer in a fashion which is easy for the end user to install and avoids awkwardness of use, reduces or eliminates errors from magnetic field changes and/or which provides output in a number of different output formats.